Maintenance Solutions
March 2008

Green Roofs: A Closer Look at Benefits

by Steve Nelson, RRC

The features of a properly constructed vegetative roof system can provide a series of advantages over conventional roof systems:

Extended roof life. The exposed waterproofing membrane of a traditional low-slope roof system is subject to deterioration from the effects of ultraviolet (UV) radiation and thermal cycling, as well as the physical damage associated with rooftop traffic, severe wind, and hail storms. So typical roofs, if well constructed and maintained, have a service life of perhaps 15-25 years.

By comparison, the protected nature of a green roof’s construction buffers the waterproofing membrane from these influences, significantly reducing the rate of membrane deterioration and potentially doubling roof life.

Energy savings. The thermal-insulating properties of green roof materials and the cooling effects of evaporation and transpiration can help regulate the roof’s surface temperatures and, in turn, reduce interior cooling requirements in warmer climates

Noise reduction. Green-roof vegetation and growing media can reduce both sound transmission and reflection, which might be important in noisier industrial or urban environments or near airports, for example.

Aesthetic appeal. Where rooftops are highly visible or accessible, green roofs can help organizations reclaim unused urban spaces for recreation, soften the view from surrounding vantage points, or help a structure blend into the natural surroundings.

Stormwater management. Increasing amounts of rapid runoff from impervious surfaces in the built environment — including rooftops — are taxing the capacity of the drainage infrastructure and increasing the potential for flooding, erosion, and pollution. Green roofs can reduce runoff by 40-90 percent, depending on its construction and the depth of growing medium, thereby reducing the stress on storm sewers.

Reduced urban heat islands. The dense development of urban environments has led to documented increases in temperatures and reductions in air quality when compared to surrounding less-developed areas. By reducing the ambient air temperature above the roof and filtering toxins from the air, vegetative roofs can help decrease this phenomenon.